Studying the impacts of climate change and ocean acidification on calcified macroalgae: why, how and what we have we found

Chris Williamson

Genomics & Microbes, Dept of Life Sciences, NHM and School of Earth and Ocean Sciences, Cardiff University

Climate change and ocean acidification (OA) are causing increased sea surface temperatures and decreased pH / carbonate saturation, respectively, in the marine environment. Almost all marine species are likely to be impacted in some respect by these changes, with calcifying species predicted to be the most vulnerable. Calcifying macroalgae of the red algal genusCorallina are widely distributed and important autogenic ecosystem engineers, providing habitat for numerous small invertebrate species, shelter from the stresses of intertidal life, and surfaces for the settlement of microphytobenthos. Given the particular skeletal mineralogy of these species, i.e. high Mg-calcite CaCO3, they are predicted to be among the first responders to OA. A research project is therefore being undertaken to examine the potential impacts of climate change and OA on Corallina species in the northeastern Atlantic. An approach has been adopted to allow examination of potential impacts in the context of present day and very recent past conditions. This seminar will present information on the approach employed (use of herbarium collections, seasonal northeastern Atlantic sampling), methodologies used (X-Ray Diffraction, PAM-fluorescence, SEM, molecular techniques), and results gained thus far (seasonal skeletal mineralogy cycles, carbonate chemistry experienced in situ, photophysiology). Plans for the next stage of the project (future scenario incubations) will also be presented, highlighting how lessons learnt thus far will inform this future work.

Forest & Nature Lab, Department of Forest and Water Management, Ghent University

Habitat change, eutrophication and climate change, among other global-change factors, have elevated the rate of species’ extinction to a level on par with historical mass extinction events. In temperate forests specifically, biodiversity is mainly a function of the herbaceous understorey community. Many forest understorey plants, however, are not able to track habitat change and the shifting climate due to their limited colonisation capacity. Their acclimation potential within their occupied habitats will likely determine their short- and long-term persistence. The response of plants to N deposition, however, diverges between forests and other ecosystems, probably due to the greater structural complexity and pivotal role of light availability in forests. A potential new pressure on forest biodiversity is the increasing demand for woody biomass due to the transitions to more biobased economies. Elevated wood extraction could result in increased canopy opening and understorey species shifts. To date, the outcome of climate warming and changing forest management (resulting in altered light availability) in forests experiencing decades of elevated N inputs remains uncertain. I will present our research on the (interactive) effects of climate warming, enhanced N inputs, and management-driven forest floor light availability on the growth and reproduction of a selection of understorey forest plant species, and (ii) the composition and diversity of understorey plant communities in European and eastern North American temperate forests.

Steve Brooks from the Museum and collaborators from UCL, the universities of Nottingham, Bergen and Liverpool, and the RSPB have been examining reasons for the breeding success of the Slavonian grebe Podiceps auritus. The Slavonian grebe has a UK breeding population of only 29 pairs, found in NE Scotland only since 1908. Loch Ruthven holds the largest British population in an RSPB reserve and breeding success is known to have fluctuated annually since records began in 1970.

The research looked at whether the fluctuations are linked to the numbers of chironomids, the group of flies on which Steve is an expert. These midges are an important food-source for the grebe chicks.

The team analysed a sediment core from the lake by slicing it into 2.5-mm sections to separate sediment on a yearly basis. In this sediment, they looked at the remains of chironomids, diatoms (planktonic algae which show strong seasonal trends in populations) and algal pigments. These plant data were used to deduce changes in total phosphorus in the water and to see whether there was a link between algae and the abundance of chironomids. Trends in grebe breeding success, chironomid abundance and algal populations were analysed against climate data to clarify whether climate was the key factor behind all of these fluctuations.

The study shows that grebe breeding success is linked with chironomid abundance and chironomid abundance is linked with total phosphorus. Over the past 100 years, lake productivity and chironomid abundance have both risen, increasing more rapidly from the mid-twentieth century to the present. Fluctuations in grebe breeding success from 1970 followed the same pattern as chironomid variation, with a lag of one year.

One of the questions of interest was whether grebe breeding success was influenced by climate variability year by year. Because the Slavonian grebe is a relative newcomer to the UK, it is not clear how vulnerable this small population is to environmental change. However. No correlation was found between grebe productivity or chironomid abundance and climate. The team concludes that breeding success of the grebe depends on food availability in the form of chironomids at Loch Ruthven.